820 THE VASCULAR SYSTEM. 
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skin and fascia, except at its termination, where it lies beneath the internal annular liga- 
ment and the origin of the abductor hallucis. 
Lateral.—The artery is accompanied by two venze comites, one on either side. The 
posterior tibial nerve lies at first on the inner side of the vessel, then crosses behind it, and 
is continued down on its outer side. In the last part of its course the artery is separated 
from the internal malleolus by the tendons of the tibialis posticus and the flexor. longus 
digitorum, whilst the tendon of the flexor longus hallucis lies behind and external to it. 
Branches.—The posterior tibial gives off numerous branches, the largest of which, 
the er al, ee one of the chief arteries of the leg. The bri ches include 
(1) Two large muscular branches which are distributed to the soleus, the tibialis 
posticus, the flexor longus digitorum, and the flexor longus hallucis. They anastomose with 
the deep sural brane shes of the popliteal artery and the lower internal articular artery. 
(2) The medullary branch (a. nutricia tibie), the largest of the medullary group 
of arteries, springs from the upper part of the posterior tibial, pierces the tibialis 
posticus, and enters the medullary foramen on the posterior surface of the tibia. In the 
interior of the bone it divides into ascending and descending branches, the former passing 
upwards towards the head of the bone, and the latter downwards towards the lower 
extremity. Before entering the tibia the medullary artery gives small muscular branches. 
(3) A communicating branch (ramus communic: ans) unites the posterior tibial to 
the peroneal artery about an inch above the inferior tibio-fibular articulation. It passes 
behind the shaft of the tibia and in front of the flexor longus hallucis. 
(4) Cutaneous branches are distributed to the skin of the inner and posterior part of 
the leg. 
(5) An internal malleolar branch (a. malleolaris posterior medialis) is distributed 
to the internal surface of the inner malleolus, anastomosing with a corresponding branch 
of the anterior tibial artery. 
(6) The peroneal artery (a. peronza, Fig. 576) is the largest branch of the posterior tibial. 
[t arises about an inch below the lower border of the popliteus, curves outwards across the 
upper part of the tibialis posticus to the postero-internal border of the fibula, along 
which it descends to the lower part of the interosseous space, and it terminates about an 
inch above the ankle-joint by dividing into anterior and posterior terminal branches. 
As the peroneal artery passes outwards from its origin it lies behind the tibialis 
posticus, and is covered posteriorly by the deep intermuscular fascia and by the soleus. 
As it descends along the postero-internal border of the fibula it lies in a fibrous 
canal between the tibialis posticus in front and the flexor longus hallucis behind. The 
peroneal artery is accompanied by two venze comites, and is crossed in front and behind 
by communicating branches between them. 
Branches.—(«) Muscular branches are distributed to the soleus, tibialis posticus, flexor longus 
hallucis, and pe ‘roneal muscles. Some pass through the interosseous membrane and supply the 
anterior muscles of the leg. 
(b) A medullary branch (a. nutricia fibule) enters the medullary foramen of the fibula. 
(c) A communicating branch (a. communicans) passes across the back of the lower end of the 
shaft of the tibia, about an inch above the inferior tibio-fibular articulation, to anastomose with 
the posterior tibial artery. 
(7d) The terminal branches are: (i.) The anterior terminal branch or anterior peroneal artery 
(ramus perforans), which passes forw: ards between the lower border of the interosseous membrane 
and the interosseous inferior tibio-fibular ligament, and runs in front of the ankle to the dorsum 
of the foot, where it anastomoses with the external malleolar branch of the anterior tibial artery 
and with the tarsal branch of the dorsalis pedis; it also supplies branches to the inferior tibio- 
fibular articulation, to the ankle- Joint, and to the peroneus tertius. 
(ii.) The posterior terminal branch (ramus calcaneus lateralis), or posterior peroneal artery, passes 
downwards behind the inferior tibio- bul: w articulation and external malleolus to the outer side 
of the heel and the foot. It supplies the ankle, the inferior tibio-fibular articulation, and the 
caleaneo-astragaloid joint, and anastomoses with the internal caleaneal branch of the external 
plantar artery, and with the tarsal and metatarsal branches of the dorsalis pedis. 
PLANTAR ARTERIES. 
(7) The internal and external plantar arteries are the terminal branches of the 
posterior tibial artery. They arise beneath the origin of the abductor hallucis 
muscle, midway be ‘tween the tip of the internal malleolus and the most prominent 
art of the inner side of the os caleis. 
Internal Plantar Artery (a. plantaris medialis),—This is the smaller of the two 
terminal branches of the posterior tibial artery. It passes forwards along the 
